1. Field of the Invention
The present invention relates to a motorcycle.
2. Description of the Related Art
A motorcycle is generally provided with a silencer. For example, the motorcycle disclosed in Japanese Laid-Open Patent Publication JP-A-2011-196242 includes an exhaust chamber and a muffler. The exhaust chamber is disposed between an engine and a rear wheel in the front-back direction of the vehicle. The muffler is disposed beside the rear wheel. The exhaust chamber and the muffler function as a silencer. Providing a plurality of silencers in this manner allows for an improvement in a silencing function.
An exhaust chamber in the motorcycle disclosed in Japanese Laid-Open Patent Publication JP-A-2011-196242 has three expansion chambers, and a chamber outlet pipe is connected to the expansion chamber that is the most downstream in the exhaust flow. As a result of this arrangement, expansion of the exhaust is repeated a plurality of times in the exhaust chambers. The passage length of the exhaust in the exhaust chambers is elongated. As a result, the noise reduction function is further improved. Moreover, an exhaust control valve is provided in the chamber outlet pipe. The amount of exhaust fed from the exhaust chamber to the muffler is controlled by opening and closing actions of the exhaust control valve.
The exhaust chamber of the motorcycle disclosed in Japanese Laid-Open Patent Publication JP-A-2011-196242 has a plurality of expansion chambers, and the chamber outlet pipe is connected to the expansion chamber that is the furthest downstream. As a result of this arrangement, while the silencing function is improved, output performance tends to be reduced especially when travelling at high speeds due to an increase in back pressure.
In order to improve output performance when traveling at high speeds, the passage surface areas of the chamber outlet pipe and of the inlet pipe in the exhaust chamber may be increased in the exhaust chamber described above. However, in this case the exhaust chamber would become much larger.
By reducing the number of expansion chambers in the exhaust chamber to one, or by reducing the exhaust passage length, the output performance of the engine when traveling at high speeds can be improved while preventing the exhaust chamber from becoming much larger. However, there is a problem that the silencing function will be reduced in this case. A good silencing function is desirable from the point of view of noise problems near the motorcycle. In particular, since a motorcycle often travels in places that are affected by noise such as urban and suburban areas when traveling at slow speeds, there is a desire for a good silencing performance at slow speeds.